The lighter the bullet weight you use? The more your shoulder will respect you....in the morning.

While that above is said somewhat in jest......it's true. Depending on the barrels rate of twist? I'd suggest somewhere in the 150gr range.
I would not attempt to 'hot rod' yer handloads. Use current loading data from a 'respected' manual. Watch for signs of 'pressure' as in flattened primers and overall case length (stretching).

If you are using a 'military' rifle? Ya might wanna have the headspace checked.....

Head space is rarely an issue on a 303 Brit since
it is a rimmed cartridge and head space is
on the rim. That said brass does not last
long since the shoulders in the rifles I loaded for
are given enough space for a hand full of sand.....

Most people only neck size .303 for target practice
to get more life out of the brass.

IMR 4895 and a Sierra flat base loaded to
about 2,000 fps should give excellent
accuracy and brass life.

I used a beam scale for several decades...worked for me, as in I ain't blind and have all my fingers.
I admit to not weighing every charge....I'd weigh ten, several times to make sure the 'drop' was correct..and go from there...generally, thousands of rounds with periodic checking. For that reason, in rifle loads, 5.56 I preferred ball/spherical powder...same in heavy hand gun loads and also used a lot of 'flake' powder like Unique for .45acp. Always a dab paranoid using Bullseye powder, double loads.

Now, on to that .303 thingy....go prone with the loads mentioned above....